Films of metals and metal oxides, particularly the heavier elements of Group VIII, are becoming important for a variety of electronic and electrochemical applications. For example, high quality RuO2 thin films deposited on silicon wafers have recently gained interest for use in ferroelectric memories. Many of the Group VIII metal films are generally unreactive toward metal oxides, resistant to diffusion of oxygen and silicon, and are good conductors. Oxides of certain of these metals also possess these properties, although perhaps to a different extent.
Thus, films of Group VIII metals and metal oxides, particularly the second and third row metals (e.g., Ru, Os, Rh, Ir, Pd, and Pt) have suitable properties for a variety of uses in integrated circuits. For example, they can be used in integrated circuits for electrical contacts. They are particularly suitable for use as barrier layers between the dielectric material and the silicon substrate in memory devices, such as ferroelectric memories. Furthermore, they may even be suitable as the plate (i.e., electrode) itself in capacitors. Iridium oxide is of particular interest as a barrier layer because it is very conductive (30–60 μΩ-cm) and is inherently a good oxidation barrier.
Capacitors are the basic charge storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and now ferroelectric memory (FE RAM) devices. They consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a dielectric material (a ferroelectric dielectric material for FE RAMs). It is important for device integrity that oxygen and/or silicon not diffuse into or out of the dielectric material. This is particularly true for ferroelectric RAMs because the stoichiometry and purity of the ferroelectric material greatly affect charge storage and fatigue properties.
The electrodes in a DRAM cell capacitor must protect the dielectric layer from interaction with surrounding materials, including interlayer dielectrics (e.g., BPSG), and from the harsh thermal processing encountered in subsequent steps of DRAM process flow. In order to function well as a bottom electrode, the electrode layer or layer stack acts as an effective barrier to the diffusion of oxygen and silicon. Oxidation of the underlying silicon will result in decreased series capacitance, thus degrading the cell capacitor. Platinum is one of the candidates for use as an electrode material for high dielectric capacitors.
Platinum, alone, however, is relatively permeable to oxygen. One solution is to combine (e.g., alloy) the platinum with rhodium to enhance the barrier properties of the layer. Physical vapor deposition (PVD) of a Pt—Rh alloy has been shown by H. D. Bhatt et. al., “Novel high temperature multi-layer electrode barrier structure for high-density ferroelectric memories,” Applied Physics Letters, 71, pp. 719–21 (1997), to provide an improvement over pure Pt for electrode applications. Also, physical vapor deposition (PVD) of a Pt—Ir alloy has been shown in JP 09162372.
Many storage cell capacitors are formed using high aspect ratio openings. PVD deposition (e.g., sputtering) does not deliver a layer which is sufficiently conformal for formation of an electrode within such a small high aspect ratio opening.
Thus, there is a continuing need for methods and materials for the deposition of metal-containing films, such as iridium- and platinum-containing films, which can function as barrier layers, for example, in integrated circuits, particularly in random access memory devices.